The effects of different densities of pigweed (Amaranthus retroflexus) on growth indices of soybean (Glycine max L.)

To evaluate the interference of Red Root pigweed on growth indices of soybean cultivars an experiment was carried out in Research, Breeding and Providing of Seedling and Seed of Karaj institute during growing season of 2002. The experiments was established as a completely randomized block design in a factorial arrangement of three soybean cultivars (L11, Clark, Pershing (Sahar)), five pigweed density (4, 8, 16, 32 plant.m-1, plus a pigweed-free control). Pure pigweed planting in 4 density consisted of (4, 8, 16, 32 plant.m-1) was considered in any replication. According to variance analysis results, pigweed caused reduction of soybean dry matter yield, leaf area index, leaf area index duration, crop growth rate and relative growth rate significantly. The maximum of dry matter yield, leaf area index, leaf area index duration, crop growth rate and relative growth rate in each three soybean cultivars reduced to control with increasing pigweed density. The maximum dry matter yield, leaf area index average, leaf area index duration and crop growth rate average in control treatment of soybean cultivars in growth duration was concerned to Pershing (Sahar) cultivar. The maximum relative growth rate average in control treatment of soybean cultivars in growth duration concerned to L11. The maximum of reduction rate of dry matter yield and leaf area index average of soybean cultivars to control occurred in Clark cultivar and its minimum occurred in Pershing (Sahar) cultivar. The maximum of reduction rate of leaf area index duration and crop growth rate average in soybean cultivars to control occurred in Pershing (Sahar) cultivar and its minimum occurred in L11. Regarding to results probability pigweed with reduction of leaf area index, leaf area index duration decreased soybean dry matter yield.